1. Field of the Invention
The present invention relates to an electro-photographic image forming apparatus and, more particularly, a toner replenishing method and unit.
2. Description of the Prior Art
In a high-speed image forming apparatus and color image forming apparatus, the toner storing section for storing toner has a large capacity, sometimes making it difficult to put it in the vicinity of a developing unit.
As a countermeasure against such a case, a toner replenishing technique is developed which conveys toner from a toner storing section to a developing unit in accordance with a toner conveying method called air conveyance that can convey the toner to a remote place (see Japanese Unexamined Patent Publication Nos. 7-219329, 10-97130, 10-268641, 10-299672, and the like).
The basic constituent elements of a toner replenishing unit utilizing air conveyance include a toner storing section, a fluid conveying means for conveying a fluid mixture of toner and air from the toner storing section, and a toner separating section for separating the toner from the conveyed fluid mixture.
In many toner replenishing units, part of the air separated from the toner is returned to the fluid conveying means without being discharged to the outside. In order to separate the toner, a filter that does not allow the toner to scatter to the outside is provided.
According to the toner replenishing technique disclosed in the above references and other Japanese Unexamined Patent Publications, the fluid mixture of the toner and air is conveyed from the toner storing section to the developing unit by a fluid conveying means such as a pump. In the prior art, a fluid conveying means comprised of a pump, which conveys the fluid mixture of air and toner from the toner storing section to the toner separating section is merely provided, and the toner conveying performance is not sufficiently high. When the toner storing section as the conveyance origin is located at a position far from the toner separating section as the conveyance destination, toner conveyance becomes difficult. Therefore, it is difficult to arrange the toner storing section at a position sufficiently away from the developing unit. In order to solve this problem, the pump must be large. When the pump is large, however, the exhaust air amount to the outside through the filter provided to the toner separating section increases. The amount of toner attaching to the filter increases, and the filter tends to undesirably clog at an early stage.
According to the conventional toner replenishing technique, as the interior of the toner separating section is in direct contact with the outside through the filter, the amount of toner filtered by the filter is large. This can cause the filter to clog at an early stage.
The present invention has been made in order to solve the problems of the toner replenishing technique utilizing conventional air conveyance, and has as its object to provide a toner replenishing method and unit with which a filter provided to a toner separating section causes less clogging and accordingly the performance of the filter can be maintained well over a long period of time, so that the storing section can be arranged away from the developing unit, and an image forming apparatus having such a toner replenishing unit.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a toner replenishing method comprising the steps of conveying, from a toner storing section which forms a fluid mixture of toner and air, the fluid mixture to a toner separating section provided away from the toner storing section through toner supplying fluid conveying means, separating the toner from air in the toner separating section, and supplying the toner from the toner separating section to a developing unit, wherein the toner replenishing method further comprises the step of returning part of the air separated from the toner from the toner separating section to the toner storing section by using returning fluid conveying means.
According to the second aspect of the present invention, when the toner is to be separated from the air in the toner separating section, the fluid mixture of the toner and air is caused to meander in the toner separating section.
According to the third aspect of the present invention, there is provided a toner replenishing unit comprising a toner storing section which forms a fluid mixture of toner and air, toner supplying fluid conveying means for conveying the fluid mixture from the toner storing section, and a toner separating section which is provided away from the toner storing section and separates the fluid mixture into the toner and air, wherein the toner replenishing unit further comprises returning fluid conveying means for returning part of the air separated from the toner from the toner separating section to the toner storing section.
According to the fourth aspect of the present invention, each of the toner supplying fluid conveying means and the returning fluid conveying means according to the third aspect comprises a transport pipe and a pump provided midway along the transport pipe.
According to the fifth aspect of the present invention, the toner storing section according to the third aspect comprises a toner hopper which is connected to a toner container for storing the toner, and a mixing chamber which is connected to the toner hopper so as to mix the toner and air.
According to the sixth aspect of the present invention, the toner storing section according to the fourth aspect comprises a toner hopper which is connected to a toner container for storing the toner, and a mixing chamber which is connected to the toner hopper so as to mix the toner and air.
According to the seventh aspect of the present invention, there is provided a toner replenishing unit comprising a toner storing section which forms a fluid mixture of toner and air, toner supplying fluid conveying means for conveying the fluid mixture from the toner storing section, and a toner separating section which is provided away from the toner storing section and separates the fluid mixture into the toner and air, the toner separating section comprising an introducing chamber where the fluid mixture is introduced and separated into the toner and air, an exhaust chamber which communicates with the introducing chamber so as to discharge air separated from the toner, and a filter which is provided to a filter chamber communicating with the exhaust chamber, wherein the introducing chamber and the exhaust chamber communicate with each other through a meandering path.
According to the eighth aspect of the present invention, the toner replenishing unit according to the seventh aspect further comprises returning fluid conveying means which returns part of the air separated from the toner from the toner separating section to the toner storing section.
According to the ninth aspect of the present invention, there is provided an image forming apparatus comprising a developing unit which performs developing by using the toner replenishing unit according to any one of the third to eighth aspects and the toner replenished by the toner replenishing unit.
According to the tenth aspect of the present invention, there is provided an image forming apparatus comprising an image forming section which has a developing unit, a sheet feeding section which is provided below the image forming section, a toner storing section which is arranged below the image forming section and on a side of the sheet feeding section and forms a fluid mixture of toner and air, a toner separating section which is arranged away from the toner storing section and in the vicinity of the developing unit, a first transport pipe which transports the fluid mixture from the toner storing section to the toner separating section, a second transport pipe which returns part of the air separated from the toner in the toner separating section to the toner storing section, a fluid mixture conveying pump which is provided midway along the first transport pipe, and a returning air conveying pump which is provided midway along the second transport pipe.
As is apparent from the above aspects, according to the present invention, the following effects which are expected to contribute to this technical field remarkably can be obtained.
The fluid is circulated between the toner storing section and the toner separating section which separates the toner from the fluid mixture conveyed from the toner storing section, by the toner supplying fluid conveying means and the returning fluid conveying means. This increases the conveying performance of the toner.
Even when the toner storing section as the toner conveyance origin is arranged away from the toner separating section as the conveyance destination, the toner can be conveyed smoothly.
In the toner separating section, the amount of air flowing to the outside decreases, so that filter clogging is suppressed effectively. As a result, the service life or cleaning period of the filter can be prolonged. In addition, since air is circulated within the toner replenishing unit, it becomes possible to be unnecessary to discharge air outside, in other words, it becomes possible to disuse any filter.
The amount of toner in the fluid mixture in a flow path extending from the toner separating section to the outside is decreased, and after that air used for conveyance of the toner is discharged to the outside through the filter. Therefore, the amount of toner deposited on the filter can be decreased. As a result, the service life or cleaning period of the filter can be prolonged.
As the toner storing section can be arranged away from the developing unit, it can store a large amount of toner. A large-capacity toner storing section, which is necessary for a high-speed image forming apparatus or color image forming apparatus, can thus be provided.
The above and many other objects, features and advantages of the present invention will become apparent to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which a preferred embodiment incorporating the principle of the present invention is shown by way of an illustrative example.